Fertilization initiates changes in the cortex, plasma membrane and glycolayx of the egg (the cortical reaction) that produce a block to polyspermy and an activation of egg metabolism. To be studied are the molecular rearrangements of the egg surface that accompany the cortical reaction in sea urchins or mammals. We will examine the mechanisms of exocytosis, the results of insertion of cortical granule membranes into the plasma membrane, and the nature of the change in the glycocalyx (vitelline membrane in sea urchins, zona pellucida in mammals) after the cortical reaction. Enzymes released during the cortical reaction will be assayed to determine the influence of selective inhibitors on cortical granule exocytosis. Plasma membrane changes will be studied by transmission electron microscopy of freeze-fracture replicas and of eggs tagged with ferritin- or hemocyanin-labeled conanavalin A and by stereological analysis of electron micrographs. The structure of the fertilization membrane will be analysed by isolation of radioactively labeled glycocalyx components. Analysis of changes in the glycocalyx will focus on the chemical nature of the cross-link formed during hardening of the fertilization membrane and the enzymes involved in the cross-linking reaction. Information gained from this study will be applied to the study of the zona reaction, examining the effects of inhibitors of fertilization membrane hardening and using the release of high specific, radioactive surface labels to examine embryos and uterine extracts for zonalytic activity.